1. Field of the Invention
The present invention relates to an x-ray system of the type having an x-ray source powered by a voltage generator and an x-ray receiver and a control arrangement for controlling the voltage generator to produce desired operating values for the x-ray source.
2. Description of the Prior Art
X-ray systems of the above type are used for registering x-ray images of stationary and moving objects. In medical applications, in order to be able to sharply display moving objects such as the heart or venous valves in x-ray images, the exposure time in the x-ray pickup--i.e. the pulse period of the x-ray pulse which is generated by means of the voltage generator and the x-ray source and which penetrates the moving object--could not be significantly longer than 10 milliseconds. Such exposure times pulse periods of x-ray pulses are achieved by large angio apparatuses such as that marketed by Siemens AG under the name "MULTISTAR," not only for single exposures of the moving object but also for cine exposures--i.e. a plurality of successive x-ray exposures in the cine mode.
The pulse technique in x-ray cinema is described by K. Boden and H. Schwesiger in "Rontgenfortschritte" 98 (1963), p. 631-635. It is explained therein that not only the pulse period but also the x-ray dose associated with the pulse are important for the achievement of equal blackening of single images in cine exposures. For the imaging of moving objects, however, the pulse period is decisive for the image sharpness of a single image or of a cine image.
German AS 11 67 456 discloses an x-ray diagnostic apparatus with a symmetrically grounded high-voltage circuit for x-ray cine exposure sequences with a grid-controlled x-ray tube and a circuit arrangement for influencing the control grid potential for controlling the x-ray tube from a blocked phase into a chronologically defined conductive phase. This apparatus demonstrates an improvement of the circuit arrangement for influencing the control grid potential of the x-ray tube.
German OS 23 04 679 teaches an x-ray diagnostic apparatus which is suitable not only for cine exposures with a film camera but also for making a single exposure with a single-image camera. To achieve this the x-ray diagnostic apparatus has an electronic image counter which is controlled by the cine camera and which triggers each x-ray exposure made by the film camera and the single-image camera for registering an x-ray image, simultaneously. The counter also actuates a unit for adjusting the dose rate of the x-ray tube to the different shutter speeds of the cine camera and the single-image camera following the end of the last image of a selectable number of film images of a cine sequence, and before the beginning of the subsequent image of the next sequence--i.e. during the period of the film transport of the film camera.
German OS 37 04 595 describes a pulsed x-ray apparatus having a circuit arrangement which effects a stabilization of the dose rate of the x-rays given voltage fluctuations of the x-ray source and which increases the effectiveness of the pulsed x-ray apparatus.
In addition, U.S. Pat. No. 5,084,912 teaches an angiography system for heart examinations which is modified such that it is also suitable for universal angiography. To this end the angiography system, for image acquisition in universal angiography, generates a number of closely successive x-ray pulses with a typical pulse period of 2 to 10 ms for heart examinations, with the single x-ray images generated by an x-ray image intensifier being accumulated by a TV camera. An image is thus acquired which corresponds to an image acquired with a single x-ray pulse with a period approximating the sum of the pulse periods of the individual x-ray pulses.
The cine mode of such x-ray systems requires the constant availability of a sufficient electrical energy to be able to generate x-ray pulses with sufficient period and x-ray energy as well as a pulse repetition rate, and thus a sufficient frame rate, for the cine mode. This requirement produces the disadvantage that such x-ray systems are usually constructed in stationary fashion, and can be connected only to certain energy supply sources, such as three-phase network terminals, which are able to make a sufficient average electrical power per unit of time constantly available for the cine mode of the x-ray diagnostic system.